This invention relates to a method and apparatus for shaping the proximal surface of a human tibia to receive a proximal tibial knee prosthesis employing a reamer/alignment guide in combination with a plateau planer instrument which cooperatively engages the guide. The planer instrument modifies the proximal tibial surface transversely with respect to the central long axis of the guide and the central long axis of the shaft of the tibia.
Various types of instruments and methods have been developed to enable a surgeon to affix a proximal tibial prosthesis to the human tibia. Such methods are generally employed in conjunction with the implantation of a total knee implant involving the implantation of both a distal femoral prosthesis and a proximal tibial prosthesis which cooperate with each other to replace a diseased or otherwise defective human knee and to restore a patient's ability to walk.
It is important that each prosthesis which is implanted be attached to the femur and tibia in such a manner that it approximates as closely as possible the natural portion of the knee which the prosthesis replaces. For example, if the proximal tibial prosthesis is not properly affixed with respect to the central long axis of the tibial shaft, an unnatural gait or other complications can result.
It is a common practice to use the long central axis of the femur as an alignment guide to determine the proper manner in which a distal femoral prosthesis is to be attached to the femur. The central long axis of the shaft of the tibia is then located and the proximal surface of the tibia is horizontally resected and prepared to receive a proximal tibial prosthesis which typically is chosen to lie in the plane of the transverse axis of the knee. If the tibial surface does not lie in the plane chosen, the implanted prosthesis may not properly align with the distal femoral prosthesis and complications can result.
One example of a method and apparatus for resecting the proximal tibial surface which employs external alignment guides situated outside of the flesh covering the femur and the tibia can be found in the "The HOWMEDICA.RTM. Universal.TM. Total Knee Instrument System", brochure no. H-2026-1 1/82 15M B (1980) from Howmedica, Inc., Orthopaedics Division, Rutherford, NJ 07070 which is hereby incorporated by reference. Another method which employs a tibial resection guide which is fixed to both the distal femoral surface and to the tibia by means of pins and employs an external alignment rod situated outside of the skin over the tibia is shown in a brochure entitled "New Jersey Tricompartmental Total Knee Replacement Surgical Procedure by Frederick F. Buechel, M.D.", 13 pages, issue date 1/1981, Form No. 1280-32, from DePuy Division, Boehringer Mannheim Corporation, Warsaw, Ind. 46580. Other examples of instruments which are intended to rest against the outside of the long axis of the tibia are the MULTI-RADIUS total knee tibial alignment guide (Catalog No. 1360-30) from Zimmer USA, Inc., Warsaw, Ind. 46580 and the Total Condylar Total Knee System tibial cutter (Catalog No. 6737-6-300) and HOWMEDICA.RTM. KINEMATIC.TM. Condylar Total Knee System tibial guide assembly (Catalog No. 6737-7-630), both of which are products of Howmedica, Inc., Orthopaedics, Division. Still another tibial alignment instrument in Catalog No. 1348-54 from Zimmer USA, Inc. which is inserted into the fixation holes for the femoral component of the GEO-PATELLA.TM./GEO-TIBIAL.TM. total knee and employs an external guide which is aligned with the tibia to mark the points where the resection should be made.
External alignment instruments have a disadvantage in that the surgeon is relying upon visual and tactile means for positioning the alignment means since the patients's skin covers the major portion of the tibia and screens it from view. Locating the shaft of the tibia of an obese person or of a person having a deformity of the tibia which may somewhat alter its true central axis can present further difficulties.